1. Field of the Invention
The invention relates to a viscous coupling of the type having a coupling housing fixed to a drive shaft, an operating chamber and a storage chamber arranged in the housing and having a fluid connection, and a valve arrangement which controls fluid flow in the connection as a function of an input rotary movement of an electromagnetic actuating device. Viscous couplings of this type are known, for example, from the field of motor vehicle technology and are used to control the rotational speed of a cooling fan connected to an internal combustion engine of a vehicle on the basis of an operating parameter, for example the cooling water temperature of an associated radiator.
2. Description of the Related Art
U.S. Pat. No. 5,152,383 discloses a viscous fluid coupling having an electromagnetic actuating device, an annular coil rotationally fixedly arranged on the side of the viscous coupling facing away from the internal combustion engine and coaxially with the drive shaft of the viscous coupling, and a rotary armature made of a ferromagnetic material in the storage chamber, which armature is rotatably arranged on a shaft and is connected to a valve disk. The rotary armature is surrounded radially on the outside by a flux guide ring. Both the rotary armature and the flux guide ring have a plurality of poles in the circumferential direction which, in an initial position, are offset from another in the circumferential direction. The flux guide ring is arranged in a housing of the viscous coupling, which can be rotated with respect to the annular coil, and extends in the axial direction as far as the immediate vicinity of a ferromagnetic housing surrounding the annular coil. If, as predefined by a controller, the annular coil is energized with a current flow, then a magnetic flux path is formed incorporating the housing of the annular coil, the flux guide ring, the rotary armature and the shaft of the latter and a rotary bearing arranged in this area, the flux path attempting to minimize its magnetic resistance. As a result, the rotary armature executes a pivoting movement from its initial position and assumes a position in which the poles are radially opposite one another in pairs. The valve disk firmly arranged upon the rotary armature can in the process, as predefined, either open or close a valve opening arranged in the fluidic connection between the operating chamber and the storage chamber. After the conclusion of the energization of the annular coil with current, the rotary armature is pivoted back into its initial position again by means of a restoring element. In the case of this configuration, there is the disadvantage that the magnetic flux path is guided over a relatively long distance, and, as a result, relatively high magnetic losses and a relatively low efficiency of the arrangement are achieved. Furthermore, the arrangement of the electromagnet on the side of the viscous coupling facing away from the internal combustion engine takes up axial space, which is generally very short in the engine compartments of modern vehicles and is generally not available.
U.S. Pat. No. 6,433,283 teaches a viscous coupling which likewise has an electromagnetic actuating device for controlling a valve opening arranged in a fluidic connection between the storage chamber and the operating chamber. Arranged on the side of the viscous coupling facing the internal combustion engine is an annular coil, which encloses a drive shaft consisting of magnetically conductive material and belonging to the viscous coupling. Arranged within the storage chamber is an armature plate made of a likewise magnetically conductive material, which is connected to a valve plate that is pivotably mounted by means of a hinge. The hub of the coupling housing, facing the annular coil, is provided with an inserted first guide ring made of magnetic material, which has one end in contact with the annular coil and, at its other end facing the operating chamber, adjoins with a gap a second guide ring of magnetic material, which passes through the rotor of the viscous coupling and ends in an area in front of the armature of the valve plate. If the annular coil is energized with a current, then a magnetic flux is formed incorporating the two guide rings, the armature plate and the drive shaft, as a result of which the valve plate executes a substantially axial movement and opens the valve opening arranged between the storage chamber and the operating chamber. In this variant, too, the magnetic circuit is very complicated in constructional terms and is configured such that it extends over a great deal of space.
The object of the invention is to provide a viscous coupling in which the magnetic losses of an electromagnetic actuating device formed within the viscous coupling are reduced and its efficiency is increased considerably with a compact design.
According to the invention, the electromagnetic actuating device includes an electromagnet and a rotary armature arranged immediately next to the electromagnet to form a magnetic flow path including the armature when the magnet is excited. The rotary armature and a closure element of the valve arrangement are fixed on a common shaft which is rotatably mounted in the housing.
By arranging the rotary armature on a shaft immediately adjacent to the electromagnet, the magnetic flux path is shortened considerably, by the actuating element being positioned closer to the magnetic field source of the electromagnetic actuating device. A likewise simple and effective forwarding of a movement of the rotary armature to the valve arrangement is achieved by the operative connection to the valve arrangement being produced by a shaft rotationally fixedly connected to the rotary armature. The magnetic flux guiding means can thus remain outside the storage or operating chamber.
In an advantageous development, the invention provides for the shaft and therefore the rotary armature to be formed radially on the coupling housing in the area of the storage chamber. In conjunction with a compact configuration of the armature, the electromagnetic actuating arrangement can overall be designed in a space-saving manner, with a very shortened magnetic flux path.
In a further improvement, the invention provides for the electromagnet to be substantially horseshoe-shaped and for its poles to be arranged spaced apart radially in relation to the drive shaft. In this way, the magnetic field source can be configured extremely compactly and efficiently.
Alternatively, with regard to the variant mentioned previously, it proves to be beneficial to form the electromagnet in the form of an annular coil. An annular coil of this type comprises a plurality of circularly executed turns of an electric conductor, which may be produced very cost-effectively.
In an advantageous development of the invention, provision is made to form a magnetically conductive housing on the electromagnet. When the electromagnet is energized, as a result, the magnetic field lines surrounding the electric conductors concentrically are focused and these can run on a predetermined path.
It proves to be beneficial to form magnetic flux guiding means on the coupling housing, this means assuming substantially the same axial position in relation to the rotary armature. As a result of this configuration, an axially shorter, that is to say more space-saving, physical extent of the electromagnetic actuating device is implemented.
If the electromagnet is energized, at least one magnetic pole is preferably formed on the housing of the electromagnet, on the side facing the coupling housing. The magnetic field originating from this pole can easily be coupled into the rotary armature or the bottom guiding means associated with the coupling housing, in order to form a closed magnetic circuit.
Furthermore, the rotary armature, the shaft and the closure element form a rotary lever device, which has a restoring element. This ensures that the electromagnetic actuating device assumes a predetermined position when not energized, and the viscous coupling changes into a predetermined operating state.
At least one stop element is advantageously provided, which limits a pivoting movement of the rotary lever device. This configuration also effects the assumption of predefined positional states of the closure element.
With regard to the embodiment mentioned previously, it is very advantageous if the electromagnetic actuating device can open the valve opening when the electromagnet is not energized, and close this opening when the electromagnet is energized. In the event of failure of a control electronics unit provided for the electromagnet or of the electromagnet itself, the viscous coupling automatically changes into an operationally safe state, the fluid contained in the viscous coupling flowing in a continuous circuit from the storage chamber through the valve opening into the operating chamber and from there, by means of a pumping element, back again into the storage chamber, and the coupling housing being driven via the fluid such that it is carried along rotationally with respect to the rotor of the viscous coupling.
In a further advantageous embodiment, the rotary armature comprises a permanent magnet. The rotary lever device created by this means automatically assumes a defined initial position, whereby the embodiment of a restoring element can be dispensed with.
It is further advantageous to arrange the electromagnet on the side of the viscous coupling facing the drive shaft. In this case, the electromagnet can, for example, be secured against rotation on an engine housing. In the case of a mounting on the engine side, the electric feed lines of the electromagnet can advantageously also be laid.
In a further variant, associated with a special advantage, the annular coil encloses a drive shaft of the viscous coupling. The electromagnet can thereby be arranged in a space-saving manner on the side facing an internal combustion engine.
In order to operate a viscous coupling, a method is advantageously used in which the intensity of the torque transmission coupling between the rotor and the housing and the rotor is set by means of pulsed energization of the electromagnet. Therefore, an actuating movement of the closure element, opening and closing the valve opening, can be controlled in such a way that, as a time average, a fluid flow is established which corresponds to any desired intermediate state of the fully opened or fully closed valve opening.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.